The present invention relates to a scroll type fluid machine that is to be used for a fluid compressor or a fluid expansion device.
As is well known in the art, scroll type fluid machines comprise a compressor housing, a fixed scroll member and a movable scroll member (orbiting scroll member). The movable scroll member is displaced relative to the fixed scroll member within the compressor housing. As the movable scroll member contacts the fixed scroll member, fluid pockets (closed spaces) are formed between the fixed and the movable scroll members. The movable scroll member is orbited while it is not allowed to self-rotate relative to the fixed scroll member. An Oldham ring is used for preventing such self-rotation of the movable scroll. The fluid pockets get smaller as they get closer to the center of the fixed and the movable scroll members, compressing the gas until it is discharged through the center of the scroll member.
As described more in detail below, the Oldham ring comprises several keys. The keys are used to fix the Oldham ring to a front end plate and an end plate of the movable scroll member within the compressor housing. Thus, it is necessary to form a keyway in, i.e., to spline the front end plate and the movable scroll member.
The front end plate and the movable scroll member are typically made of iron-based material. In order to form a keyway in, for example, the front end plate, the latter is cut into a desired shape. The front end plate is then ground and splined. The front end plate may be subjected to heat treatment upon formation of the keyways.
Surface finishing with high accuracy is involved in the formation of the keyways to prevent seizure or abnormal abrasion or wear of the keys. To this end, cutting, grinding, and the heat treatment should be made. These works deteriorate productivity of the keyways, increasing the manufacturing cost for them. The heat treatment causes strain in the keyways, which may make it difficult to assemble the keys.
Problems arise when the movable scroll member is subjected to heat treatment upon formation of the keyways. When the movable scroll member is heated after being cut, the movable scroll member would be deformed. On the contrary, when the movable scroll member is heated before being cut, subsequent processes would be more difficult.
The front end plate and the movable scroll member may be made of the iron-based material, taking the wear resistance into consideration. However, such the iron-based material increases the weight of the fluid machine itself.